Process for plating aluminum alloys with manganese

ABSTRACT

There is provided a process for electroplating of manganese containing aluminum alloys with manganese. In the process a tenacious bond of manganese metal to the alloy is achieved because the formation of a deposit of the oxides of manganese which have a low bond strength to aluminum and which readily flake from an aluminum surface is avoided. The product produced may be converted by oxidation to a catalytic surface converting ozone to oxygen, the oxides of nitrogen to inert nitrogen as well as the conversion of carbon monoxide to carbon dioxide.

United States Patent [191 Behl [ Oct. 16, 1973 PROCESS FOR PLATING ALUMINUM ALLOYS WITH MANGANESE [76] Inventor: Betty A. Behl, 2071 Midwick Dr.,

Altadena, Calif. 91001 [22] Filed: Apr. 17, 1972 I [21] Appl. No.: 244,927

[52] U.S. Cl. 29/197, 29/198, 204/45 R [51] Int. Cl C23b 5/30, B23p 3/00 [58] Field of Search 204/45 R, 105 M;

[56] References Cited UNITED STATES PATENTS 6/1943 Fink et al 204/45 R 4/1946 Bradt et a1. v. 204/45 R OTHER PUBLICATIONS Harold H. Oaks et al., Trans. American Electrochemical Soc., Vol. 69, pp. 567583, (1936).

Primary ExaminerG. L. Kaplan Attorney-Robert L. Parker et a1.

[ 5 7 ABSTRACT bond strength to aluminum and which readily flake from an aluminum surface is avoided. The product produced may be converted by oxidation to a catalytic surface converting ozone to oxygen, the oxides of nitrogen to inert nitrogen as well as the conversion of carbon monoxide to carbon dioxide.

10 Claims, N0 Drawings PROCESS FOR PLATING ALUMINUM ALLOYS WITH -MANGANESE BACKGROUND OF THE INVENTION Aluminum has been well known to be an extremely difficult metal to electrolytically plate. Special methods for pretreating the aluminum surface to achieve a deposit of a metal have been practiced and well published. Despite the preparation procedures employed the bond strength of the deposited metal to the aluminum surface has normally been low.

Where manganese is employed as a metal for electrolytic deposition onto aluminum, it has been found that despite the pretreatments employed or modifications of the electrolytic solution used, either incomplete deposition of manganese onto the surface or deposition of manganese in an oxidized state occurs.

In the former, the non-uniform deposition of manganese renders the surface of limited value where complete manganese deposition is desired.

In the latter, where manganese is deposited as an oxide, the adhesion to the surface of the metal is extremely low, rendering the coated surface susceptible to readily flaking away of the deposit upon any flexule movement of the-plated surface.

SUMMARY OF THE INVENTION It has now been found that an extremely tenacious bond of pure manganese may be deposited on the surface of an aluminum alloy provided there is present within the alloy a certain amount of manganese. It has also been observed that the presence of copper in the alloy or the presence of copper in the plating tank enhances electrolytic deposition and adhesion of manganese to the surface of the alloy without the initial formation of an oxide of manganese.

Following electrolytic deposition of the manganese metal the applied coating may be readily converted to the oxides of manganese such that the plated surface will be active with respect to the conversion of ozone to oxygen, the oxides of nitrogen to inert nitrogen, as well as the oxidation of carbon monoxide to carbon dioxide and other reactions.

The plating process comprises, in general, immersing the aluminum alloy to be plated in an alkaline solution, such as a solution of sodium hydroxide, to remove any oxides present on the surface of the alloy to be plated.

The alloy, after a water. rinse, is then immersed as a cathode in a plating tank where there is provided as the anode manganese metal in a pure or impure state and in which the electrolyte is a solution of an acidic salt of manganese such that the anion of the salt will attack the manganese metal to make it available for deposition onto the surface of the aluminum alloy.

In general, the aluminum alloy to be plated should contain at least about l.2 percent manganese and it is preferred that either the alloy or the tank in which plating occurs contains some amount of copper.

Plating occurs at amperage rate of about 1 to about 2 amps per hundred square inches of alloy surface with convert the deposited manganese to manganese dioxide.

It is a main feature of the present invention, however, that due to the presence of manganese in the aluminum alloy that the initial deposit will be pure manganese as opposed to manganese in some state of oxidation. As a consequence, the adhesion of the manganese to the surface is extremely high and subsequent oxidation of the deposited coat will not decrease the bond strength developed.

Where aluminum free of manganese is employed, in contrast, the manganese will tend to deposit in an oxide form and readily flake from the aluminum surface.

DETAILED DESCRIPTION According to the present invention, there is provided a process for providing a tenacious bond of manganese onto aluminum alloys which contain as an ingredient thereof, manganese metal. Deposition of a pure coat of manganese is further enhanced by the presence of copper, either in the ,alloy or in the electrolytic tank in which the electrolytic deposit occurs.

As a particular of the invention there is involved electrolytic deposition of a manganese honeycomb aluminum structure for ultimate use as a catalytic converter for elimination of ozone, the oxides of nitrogen, and carbon monoxide from the gas streams.

The problem primarily presented was the ability to obtain a tenacious bond of-essentially pure manganese to the surface of the honeycomb.

It has been found that employing as the substrate to be electroplated an alloy manufactured by Aluminum .Corporation of America and known as Alloy 3003,

which contains as alloy ingredients about 0.1 percent copper and about 1.2 percent manganese, the remainder being aluminum and impurities, that a uniform plate of manganese on an oxide free surface is achievable. Aluminum alloy 3003 has an accepted industrial composition as published by Engineering Aluminum Digest, Upper Montclair, N.J., Sept. 1955, Filing Code A1:3l as containing Manganese in an amount of from about 1.0 to about 1.5 percent by weight, Copper up to about 0.2 percent by weight, Iron up to about 0.7 percent by weight, Silicon up to about 0.6 percent by weight, Zinc up to about 0.1 percent by weight, other elements up to about 0.15 percent by weight, the remainder being Aluminum.

As will be shown in the foregoing examples, this alloy is readily receptive to the deposition of an essentially pure plate of manganese as opposed to a plate of oxides of manganese which have poor adhesion to the surface to obtain a strong bond of manganese to the alloy which can be readily converted to MnO for use as a catalytic surface in a system for removing the aforementioned impurities from a gas stream.

In the basic plating operating, the manganese containing aluminum alloy serves as a cathode while manganese metal serves as the anode.

The electrolyte employed for the deposition process is an aqueous solution of one or more acidic salts of manganese. Generally, the preferred salts are manganese sulfate and manganese chloride with the latter being particularly preferred.

Normally solution concentration of the acid salt is from 0.5 to about 2.0 molar, preferably about one molar.

Current densities during the electrodeposition may range from about 1 or less to about 2 or more amperes per 100 square inches of surface of the aluminum alloy to be plated for a distance between the anode and cathode of about 4 inches.

The voltage applied is only that required to maintain the desired current flow for resistance provided.

Plating can be carried at ambient temperatures or at elevated or lower temperatures as desired.

It is preferred, however, that the lower end current density range be employed as it has been found that adhesion of manganese to the alloy will be maximized at lower plating rates which is a direct function of current density.

While copper is not a necessary ingredient of either the alloy or the tank in which manganese deposition occurs, its presence has also been found to enhance adhesion of the manganese to the surface of the alloy.

Unless the alloy is provided in a clean state, a predicate to the electrodeposition process is to treat the alloy with a base to remove any oxides, oils and the like existing on the surface of the alloy. This may be conveniently accomplished by immersion of the alloy into a base such as sodium hydroxide to remove any oxides present as well as any organic materials which may be present on the alloy surface.

Following this, the alloy is simply rinsed in water and immersed into the electrolytic deposition tank in which deposition of pure manganese onto the surface of the alloy occurs.

Following deposition of the manganese onto the surface of the alloy to the extent required, the coated alloy is removed and, for general purposes, the surface is oxidized for use as a catalytic surface for conversion of ozone and the oxides of nitrogen to oxygen and inert nitrogen as well as the conversion of carbon monoxide to carbon dioxide.

Surface conversion of manganese to manganese dioxide may be simply carried out by contact with air or a peroxide solution.

Another convenient method of conversion is to contact the deposited manganese with a solution of hydrochloric acid, generally of a concentration ofabout 0.1 normal to convert the manganese to manganese chloride followed by contact with a solution of sodium hydroxide, generally in the concentration of about 0.2 molar to convert the manganese to manganese hydroxide followed by contact with a peroxide solution to produce a manganese dioxide coating.

The following example and control are illustrative of the practice of the invention to indicate the peculiarities in the presence of manganese as an alloy in aluminum to achieve the deposition of manganese as required in accordance with the practice of this invention.

EXAMPLE 1 An aluminum alloy honeycomb structure measuring X 10 X K and composed of interconnected hexagonal cellshaving wall spacing of three-eighths inch was employed as the cathode for electrodeposition of manganese. The alloy designated as Alloy 3003 manufactured by Alcoa and was composed of 0.12 percent by weight copper, 1.2 percent by weight manganese, the balance being aluminum and impurities.

The honeycomb structure was first cleansed with a 1.0 N solution of NaOH until effervesence occured,

rinsed in water, then placed in an agitated electrodeposition tank containing a solution 0.1 M MnCl as the electrolyte and manganese metal.

The honeycomb structure served as the cathode and the manganese as the anode. Spacing was 4 inches. After plating for 1 hour at a current flow of 1.25 amperes there was deposited a uniform coat of manganese. The manganese was firmly bonded to the aluminum surface. After contact with air the manganese turned black indicating its conversion to MnO Control A The procedure of Example 1 was repeated except the electrolyte solution also contained 120 grams Nl-hCl per 20 liters of solution as is suggested in U.S. Pat. No. 2,398,614 to Bradt et al. to enhance adhesion. Current flow was 1.255 amperes and plating time was 2 hours. There was less than 15 percent deposition of manganese on the surface and considerable oxidation of the aluminum surface was evident.

Control B The procedure of Example 1 was repeated except that the honeycomb did not contain manganese as an alloy constituent. Only about 30-35 percent of the surface accepted a plate of manganese and it deposited in an oxide state. As a consequence the oxide readily flaked from the cell surfaces.

Control C Control B was repeated except that plating time was increased to 2 hours. There was little increase in the amount of manganese deposited. Again, because of initial oxide formation, the deposited manganese had a poor adhesion for the aluminum surface and readily flaked from it.

What is claimed is:

'1. A process for electroplating manganese onto aluminum which comprises providing a flow of current in a plating tank between a cathode which is a manganese containing alloy of aluminum having the composition: manganese from about 1.0 to about 1.5 percent by weight, copper up to about 0.2 percent by weight, iron up to about 0.7 percent by weight, silicon up to about 0.6 percent by weight, zinc up to about 0.1 percent by weight, other elements up to about 0.15 percent by weight, the balance being aluminum, and a manganese anode in an electrolyte which is an aqueous solution of an acidic salt of manganese essentially free of ammonium ion for a time sufficient for a deposit of pure manganese to form on the alloy surface.

2. A process as claimed in claim 1 in which the alloy of aluminum contains at least about 1.2 percent by weight manganese.

3. A process asclaimed in claim 2 in which copper is present in the alloy.

4. A process as claimed in claim 2 in which manganese plating is carried out at a current density of from about 1 to about 2 amperes per square inches of alloy surface.

5. A process as claimed in claim 1 in which the acidic salt of manganese is manganese chloride.

6. A process as claimed in claim 5 in which the manganese chloride concentration in solution is about 0.1 molar.

7. A process as claimed in claim 6 in which manganese plating is carried out at a current density of from about 1 to about 2 amperes per 100 square inches of alloy surface.

3,765,847 s I 6 8. A process as claimedin claim 1 in which copper is about 1 to about 2 amperes per 100 square inches of present in the plating tank. alloy surface.

9. A process as claimed in claim 1 in which manga- 10. The product of the process defined in claim 1. nese plating is carried out at a current density of from 

2. A process as claimed in claim 1 in which the alloy of aluminum contains at least about 1.2 percent by weight manganese.
 3. A process as claimed in claim 2 in which copper is present in the alloy.
 4. A process as claimed in claim 2 in which manganese plating is carried out at a current density of from about 1 to about 2 amperes per 100 square inches of alloy surface.
 5. A process as claimed in claim 1 in which the acidic salt of manganese is manganese chloride.
 6. A process as claimed in claim 5 in which the manganese chloride concentration in solution is about 0.1 molar.
 7. A process as claimed in claim 6 in which manganese plating is carried out at a current density of from about 1 to about 2 amperes per 100 square inches of alloy surface.
 8. A process as claimed in claim 1 in which copper is present in the plating tank.
 9. A process as claimed in claim 1 in which manganese plating is carried out at a current density of from about 1 to about 2 amperes per 100 square inches of alloy surface.
 10. The product of the process defined in claim
 1. 